1. Field of the Invention
The present invention relates to an objective lens used for performing recording, reproduction and deletion of information on an optical information recording medium, and to an optical pickup device employing this objective lens.
2. Description of the Background Art
In the conventional art, optical disk units capable of writing information onto an optical disk such as a CD medium and a DVD medium, reading information from an optical disk, and deleting information recorded on an optical disk are widely used. In such optical disk units, an optical pickup device that includes an objective lens is employed (see, for example, Japanese Laid-Open Patent Publication No. 2003-91854).
In recent years, Blu-ray Disc (registered trademark) employing a blue laser has been developed and has caused the necessity of an objective lens having a remarkably high numerical aperture (NA=0.85). When such an objective lens is to be realized, the thickness of the objective lens need remarkably be increased in general. This causes an increase in the load to the actuator for driving the objective lens. Further, a problem also arises that the high NA causes notable occurrence of off-axial aberration and coma aberration resulting from decentering. Further, in such an objective lens having a remarkably high NA, the inclination angle of the lens surface increases. This causes difficulty in fabrication of a molding die for objective lens manufacturing and in molding of an objective lens.
Thus, an object of the present invention is provide an objective lens in which even in case of a remarkably high NA, thickness reduction and weight reduction are achieved, while satisfactory mass productivity is obtained.